What is this Genesis Hardware?!

[Jeffrey]

I found this part attached to a Genesis (model 2) in a thrift store. It was a bump sticking out the side attached to the expansion port, noticeable because it was much larger than the normal dust cover.

A quick internet search shows a similar item on ebay being listed as a 32x component. (here's a link http://www.ebay.com/itm/Sega-32x-Genesis-EXTENSION-EXPANSION-Unit-Cover-/220779669855)

That can't be right because I have a used 32x that seems to work just fine without it. It didn't have any other ports or cable holes, so it doesn't seem to be a Sega CD adapter. Is it a modem part?

I didn't get to buy the part because the lady suddenly became suspicious and wanted huge money for it (she thought it was something extremely valuable because of my interest). What is it? What does it do? Should I go back and get it?

 

[Kuta]

The expansion slot on the side was mainly intended for connecting the Mega CD unit. What's on the other side? If nothing then it may contain memory for saving games.

 

[Chilly Willy]

That's a bus terminator pack for the CD expansion port. Certain revisions of the 32X wouldn't work if you didn't have the CD expansion, so the bus terminator was included for people without the CD. You would plug in the 32X like normal, and plug that part into the CD expansion on the side. The part itself is fairly worthless and can be gotten pretty cheap unless you run into some greedy idiot like the one you described. If you have a CD, the part is not needed, so people often sell those parts separate from the 32X.